On both sides of the U.S.-Mexico border , key questions are lingering after Mexico 's presidential vote .

Election authorities projected Enrique Peña Nieto of the Institutional Revolutionary Party , or PRI , as the winner Sunday night . But his closest competitor , Andres Manuel Lopez Obrador of the Democratic Revolution Party , or PRD , has not conceded .

The election results raise issues rooted in Mexico 's complicated political past that will play a critical role in shaping the nation 's future , analysts say .

Has the PRI , a political party that critics accuse of being authoritarian and corrupt , changed its approach in Mexico ? Will Lopez Obrador and his supporters protest the election results as they have in the past ? And will Peña Nieto 's proposal to decrease violence mark a significant shift in U.S.-Mexico drug war policy ?

Mexico 's old guard is back

On the local level , there may not be many differences between today 's PRI and the political party that dominated Mexico for decades , said Andrew Selee , director of the Mexico Institute at the Woodrow Wilson International Center for Scholars .

`` What 's changed on the national stage is that Mexican citizens have different expectations for their federal government that are going to force the PRI to govern in a different way than it did 20 years ago , '' Selee said .

`` Then , the PRI was really a party that included all of Mexico , that had a broad patronage network and tolerated little dissent outside of the party . And the PRI today is going to have to deal with opposition parties that have tasted power , an active citizenry that expects to be involved in major policies decisions and a very vigilant press that will report on everything that happens . ''

Sunday 's election was closer than many expected , Selee said , and Peña Nieto and PRI party leaders realize they secured a narrow victory .

`` I get the sense the PRI recognizes that they are going to have to build broader coalitions in order to govern effectively , '' he said .

Only time will tell , said Jorge Chabat , a professor at Mexico 's Center for Research and Teaching in Economics .

`` The truth is that we do n't know very well who the PRI is now , '' he said .

And it 's unclear how influential leaders from the party 's old guard -- some of whom have close ties with Peña Nieto -- will be , he said . In the past , presidential candidates have said one thing on the campaign trail , then done something else in office .

`` We do n't really know how he is going to behave . ... Now we are going to see , who is Peña Nieto , truly ? '' Chabat said .

U.S. Rep. Henry Cuellar , a Democrat from the border city of Laredo , Texas , said the answer is clear .

`` He is different . He is a young , outgoing personality , '' said Cuellar , who describes Peña Nieto as a friend and flew to Mexico City over the weekend to support the candidate . `` He 's from a young , new generation . He 'll bring a lot of fresh , new ideas . ''

An ` explosive ' mixture ?

Critics of the 45-year-old former governor are n't convinced .

Weeks before Sunday 's vote , criticisms of Peña Nieto and concerns about the PRI 's possible return to power fueled a student movement that has staged demonstrations throughout the country .

`` There 's a lot of angry voters . The question mark is , what are they going to do ? '' said Ana Maria Salazar , a security analyst and former Pentagon official who lives in Mexico City .

In 2006 , Lopez Obrador 's supporters protested nationwide after election authorities said he narrowly lost to Felipe Calderon in presidential elections .

How will PRI 's win change the U.S.-Mexico relationship ?

Lopez Obrador claimed election fraud and never conceded , referring to himself as `` the legitimate president of Mexico . '' In Mexico City , his followers staged massive sit-ins and blockades .

It 's unclear , Salazar said , whether protesters will take a similar approach this time around , or try something more severe .

`` In a country like Mexico , where we already have a high incidence of violence due to organized crime , add to that social unrest , and it could be an explosive mixture , '' she said . `` I certainly hope not , but we will soon find out . ''

The Mexico Institute 's Selee said Lopez Obrador 's reaction Sunday night signaled that any protests this year are likely to be less intense .

The former Mexico City mayor was measured In response to the results of Sunday night 's quick count , which placed him at least 6 percentage points behind Peña Nieto . Rather than relying on the quick count , which is based on samples from polls nationwide , Lopez Obrador said he would wait for results from the final official vote tally , which begins Wednesday .

`` We are going to have all the information and at that time we will establish a position , '' he said .

After the 2006 vote , which gave Calderon a narrow victory margin of less than 1 % , Lopez Obrador was quick to declare fraud .

The difference in reaction is significant , Selee said Monday .

`` The fact that Lopez Obrador did not call for mobilization last night means that he 's already tipped his hand to accepting the results when they come out . He essentially demobilized his supporters , '' Selee said .

A different drug war approach ?

Beyond Mexico 's borders , part of Peña Nieto 's campaign platform has been a focal point for U.S. officials and lawmakers : Peña Nieto 's pledge to focus more on reducing violence and less on catching cartel leaders and blocking drugs from reaching the United States .

`` I am convinced that in terms of security , we need to adjust the policy to keep confronting organized crime , criminal gangs and cartel chiefs head-on , '' Peña Nieto told CNN en Español Monday . `` But we also have to search for a strategy , a reduction of violence in this country . ... The strategy we follow in the short term clear signs of better effectiveness and a reduction in crime rates . ''

Announcing a crackdown on cartels and sending troops into the streets to help fight the battle were among the first major moves by Calderon after he took office in December 2006 .

And for nearly six years , a brutal drug war in Mexico with a staggering death toll of more than 47,500 people has dominated discussions between the United States and Mexico .

Some political opponents of Pena Nieto , whose party governed Mexico for more than 70 years until 2000 , have warned that negotiating with drug cartels and gangs could be on his agenda -- an accusation that Peña Nieto has repeatedly denied .

But his denials have n't squelched speculation on both sides of the border that negotiating with cartels -- or at least easing the pressure on them -- could be on the table .

In a congressional hearing last month , U.S. Rep. Jim Sensenbrenner said the war on drugs was nearing a `` potential crossroad , '' referring to Peña Nieto 's plan and his party 's political history .

`` While in power , the PRI minimized violence by turning a blind eye to the cartels , '' the Wisconsin Republican said , noting that Peña Nieto `` does not emphasize stopping drug shipments or capturing kingpins . ''

In a statement the next day , Peña Nieto 's campaign said he was committed to combating organized crime .

`` The law is applied ; it is never negotiated , '' the statement said .

Cuellar , the Texas congressman , said this week that such concerns from Sensenbrenner and other lawmakers were unfounded . Changing strategies in dealing with drug violence , Cuellar said , does n't mean stopping the battle .

`` I asked him about it . ... He told me , ` I 'm gon na fight it . I want to use a different strategy , ' '' Cuellar said , noting that relations between the United States and Mexico would likely strengthen under Peña Nieto 's leadership .

Pledges to change tack in the drug war were common across party lines on the presidential campaign trail this year , Chabat said .

`` In the end , I do n't think he will do many things differently than Calderon , because there is n't much that can be done differently , '' Chabat said . `` There 's not a lot of room to work . In speeches , it sounds really great to say that you 're going to do things differently , but there wo n't be many changes . ''

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Projected winner Enrique Peña Nieto says he remains committed to cartel fight

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Former Pentagon official : Social unrest after the election `` could be an explosive mixture ''

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Analyst : Mexicans `` are going to force the PRI to govern in a different way ''

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Peña Nieto says he 's part of a new generation , but critics are n't convinced